Perpendicular media with dual soft magnetic layers

ABSTRACT

A recording medium having a substrate, a first soft magnetic underlayer, a second soft magnetic underlayer and a perpendicular magnetic recording layer without a spacer layer between the first and second soft magnetic underlayers is disclosed.

FIELD OF INVENTION

This invention relates to perpendicular recording media, such as thinfilm magnetic recording disks having perpendicular magnetic anisotropy,and to a method of manufacturing the media. The embodiments of theinvention have particular applicability to perpendicular media havingfirst and second magnetic underlayers (SUL) without a spacer layerbetween the two layers of the dual SUL or between laminations of theSUL.

BACKGROUND

Perpendicular magnetic recording systems have been developed for use incomputer hard disc drives to provide higher liner density thanlongitudinal recording. FIG. 1, obtained from Magnetic Disk DriveTechnology by Kanu G. Ashar, 322 (1997), shows magnetic bits andtransitions in longitudinal and perpendicular recording. In alongitudinal recording there exists a demagnetization field between twomagnetic bits. These demagnetization fields tend to separate bits,making transition space between bits, that is, transition parameter a,large as shown in FIG. 1 (a). At very high bit densities, the limitingparameter may be the length of the transition region. Perpendicularrecording bits do not face each other, and hence they can be written atclosed distances as shown in FIG. 1 (b).

A typical perpendicular recording head includes a trailing write pole, aleading return or opposing pole magnetically coupled to the write pole,and an electrically conductive magnetizing coil surrounding the yoke ofthe write pole as shown in FIG. 2, Magnetic Disk Drive Technology byKanu G. Ashar, 323 (1997). The ring-type head shown in FIG. 2 isgenerally not used for perpendicular recording anymore. The writerportion of the head is still being used, but the reader portion is not.Perpendicular recording media may include magnetic media and anunderlayer as shown in FIG. 2. The magnetic media could be a hardmagnetic recording layer with vertically oriented magnetic moment andthe underlayer could be a soft magnetic underlayer to enhance therecording head fields and provide a flux path from the trailing writepole to the leading or opposing pole of the writer. The magnetic fluxpasses from the write pole tip, through the hard magnetic recordingtrack, into the soft magnetic underlayer, and across to the opposingpole. Such perpendicular recording media may also include a thininterlayer between the hard recording layer and the soft magneticunderlayer to prevent exchange coupling between the hard and softlayers. The soft magnetic underlayer helps also during the readoperation. During the read back process, the soft magnetic underlayerproduces the image of magnetic charges in the magnetically hard layer,effectively increasing the magnetic flux coming from the medium. Thisprovides a higher playback signal.

The soft magnetic underlayer is located below a recording layer andalters the flux path from the recording head main pole to the returnpole. For a thick, high permeability SUL, the altered flux path issimilar to that which would result from placing a mirror image of therecording head below the SUL surface. Thus, the net recording field atthe hard magnetic recording layer becomes fairly large compared to thefield generated in the case of longitudinal recording. Magnetic fluxflows from head through the SUL to return pole crossing twice throughthe recording layer. The quality of the image, and therefore theeffectiveness of the soft magnetic underlayer, depends upon thepermeability of the soft magnetic underlayer.

Conventional perpendicular magnetic recording media comprise magneticSUL, seed layers, HCP (Hexagonal Close Packed)-structured interlayers,Co-based magnetic recording layers, and carbon overcoat. The SUL hassignificant effect on the crystallographic orientations of the recordinglayers. Some typical materials used as SUL such as FeCo_(30.5)B_(12.8),feature high saturation induction, Bs, moderate magnetic permeability,μ, and provide an appropriate template for the seed layers, interlayers,and recording layers to grow on. The magnetic performance andcrystallographic structure of the media with such SUL are generallyreasonable. However, media yields often suffer due to a higher incidenceof target spitting. Also, in order to suppress stripe domain formationin SULs featuring high magnetostriction constant, including FeCoB, alaminated SUL structure with spacer layers, such as Ta, could beinterposed between critically thin soft layers. The medium issputter-deposited under room temperature, which is the typical processtemperature for granular recording media. Each spacer layer needs onedeposition chamber and requires an additional deposition step. It istherefore advantageous to have a perpendicular recording medium withouta spacer layer between SUL laminations or to eliminate the need forlamination by the use of appropriate SUL materials that suppress stripedomain.

SUMMARY OF THE INVENTION

Some embodiments of this invention show that the SUL not only providesthe path for the return of magnetic flux to the writer head, but alsoaffects the crystallographic orientation of the HCP-structuredinterlayer and magnetic recording layers. The hard magnetic recordinglayer crystallographic orientation depends more strongly upon the topportion of the SUL. In order to provide a high permeability path for themagnetic flux to be returned to the writer head, the product of thesaturation magnetic induction, Bs, and the thickness of SUL, t, could bemore than certain minimum value, for instance, 0.001 Gauss·meter.

Besides satisfying the requirement on Bs, μ, corrosion resistance of theSUL, according to embodiment of the invention, the top SUL is selectedfor providing good crystallographic orientation of the interlayer andmagnetic recording layers, and the bottom SUL is selected to have lowmagnetostriction constant to make a thick enough SUL to satisfy therequirement on Bst of SUL. The dual SUL also enables removal of spacerlayers between laminated dual SUL structures in the prior art. The dualSUL of the invention also enables use (as a first SUL) of a class of SULmaterials that have many desirable properties, but do not provide goodhard magnetic recording layer orientation when used as a single or toplayer (second) SUL. The bottom SUL is selected also to have less chanceof target spitting (defect formation on the discs) to improve the glideyield of the media with or without spacer layers.

By employing SUL with two or more kinds of materials, the effectivepermeability of the SUL can be tailored to a suitable value by adjustingthe thickness ratio of the component SUL materials.

The embodiments of the invention are directed to a perpendicularrecording medium having a SUL structure, which provides theperpendicular magnetic recording media with good magnetic performancesand reduced yield loss due to spitting. The SUL structure in oneembodiment does not need a spacer layer between the layers of the SULstructure.

One embodiment of this invention relates to a perpendicular recordingmedium, comprising a substrate, a first soft magnetic underlayer, asecond soft magnetic underlayer and a magnetic recording layer without aspacer layer between the first and second soft magnetic underlayers,preferably wherein the first and second magnetic underlayers containsubstantially no stripe domains and the combined Bst of the first softmagnetic underlayer and the second soft magnetic underlayer is greaterthan 0.002 Gauss·Meter.

Another embodiment relates to a method of manufacturing a perpendicularrecording medium, comprising obtaining a substrate, depositing a firstsoft magnetic underlayer, depositing a second soft magnetic underlayerand depositing a magnetic recording layer without a spacer layer betweenthe first and second soft magnetic underlayers.

Yet another embodiment relates to a perpendicular recording medium,comprising a substrate, a first soft magnetic underlayer, a second softmagnetic underlayer and a magnetic recording layer, wherein the firstsoft magnetic underlayer comprises a material with an absolute value ofmagnetostriction constant of less than 5*10⁻⁶, wherein the material isselected from the group consisting of CoZrNb, CoZrTa, and combinationsthereof, preferably wherein the magnetic recording layer has a growthdirection with less than 4° FWHM of XRD rocking curves around (0002)peaks.

As will be realized, this invention is capable of other and differentembodiments, and its details are capable of modifications in variousobvious respects, all without departing from this invention.Accordingly, the drawings and description are to be regarded asillustrative in nature and not as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows (a) longitudinal and (b) perpendicular recording bits.

FIG. 2 perpendicular pole head with magnetic media and underlayer.

FIG. 3 is a schematic of an embodiment of a perpendicular recordingmedium of this invention.

FIG. 4 shows erasure of media with three kinds of SUL of samples D, E,and F, listed on Table II.

FIG. 5 shows optical HDI images of samples C (top), D (Middle) and F(bottom) on table II measured with p-polar channel and in phase modedisplay range 10.

DETAILED DESCRIPTION

The embodiments of the invention provide a perpendicular recordingmedium that could have ferromagnetic and antiferromagnetic coupling in asoft magnetic underlayer of the perpendicular recording medium. Theembodiments of the invention are particularly suitable for use with amagnetic disc storage system with a recording head having a head capableof performing read and write operations. Antiferromagnetic couplinggenerally refers to the coupling between ferromagnetic layers ormultilayer structures such that adjacent ferromagnetic layers ormultilayer structures have magnetizations that point in generallyopposite directions. Ferromagnetic coupling generally refers to indirectcoupling between ferromagnetic layers or multilayer structures such thatadjacent ferromagnetic layers or multilayer structures havemagnetizations that point in generally the same directions.

A preferred embodiment of a perpendicular recording medium of thisinvention is shown in FIG. 3. The adhesion layer 11 is about 2.5 to 4.0nm. The thickness of seedlayer 17 is about 1 to 5 nm, preferably, about1.5 to 3 nm. The total thicknesses of the first and second soft magneticunderlayers 12 and 13 are preferably greater than 50 nm, morepreferably, about 100 to 200 nm, and the thickness of magnetic recordinglayer 15 deposited on the underlayer is about 7 to 20 nm. There is nospacer layer between the first and second soft magnetic underlayers. Inbetween the second amorphous soft magnetic underlayer 13 and themagnetic recording layer 15 could be an interlayer 14 of thickness ofabout 5 to 35 nm. Protective layer 16 typically covers the magneticrecording layer 15.

The embodiments of the invention provide magnetic recording mediasuitable for high areal recording density exhibiting high SMNR. Theembodiments of the invention achieve such technological advantages byforming a soft magnetic underlayer. A “soft magnetic material” is amaterial that is easily magnetized and demagnetized. As compared to asoft magnetic material, a “hard magnetic” material is one that neithermagnetizes nor demagnetizes easily.

The underlayer is “soft” because it is made up of a soft magneticmaterial, which is defined above, and it is called an “underlayer”because it resides under a recording layer. In a preferred embodiment,the soft layer is amorphous. The term “amorphous” means that thematerial of the underlayer exhibits no predominant sharp peak in anX-ray diffraction pattern as compared to background noise. The“amorphous soft magnetic underlayer” of the embodiments of the inventionencompasses nanocrystallites in amorphous phase or any other form of amaterial that exhibits no predominant sharp peak in an X-ray diffractionpattern as compared to background noise.

When soft magnetic underlayers are fabricated by magnetron sputtering ondisk substrates, there are several components competing to determine thenet anisotropy of the underlayers: effect of magnetron field,magnetostriction of film, stress originated from substrate shape andtopography, thermal expansion coefficients, etc. The first and secondsoft magnetic underlayers can be fabricated as single layers ormultilayers.

The soft magnetic underlayer could be deposited from targetsmanufactured by a gas atomized, alloyed powder process (AP) or by amolten material casting into a mold at a temperature between 1200 to1550° C., and solidifying into an ingot. The ingot could then pre-heatedto a temperature between 850 and 1200° C. in an annealing furnacesuitable for rolling to desired thickness for final machining to precisetarget size.

An adhesion layer is a layer lying in between the substrate and theunderlayer. Proper adhesion layer can also control anisotropy of thesoft magnetic underlayer by promoting microstructure that exhibit eithershort-range ordering under the influence of magnetron field or differentmagnetostriction. An adhesion layer could also alter local stresses inthe soft magnetic underlayer.

Preferably, in the soft magnetic underlayer of the perpendicularrecording medium of the embodiments of the invention, an easy axis ofmagnetization is directed in a direction substantially transverse to atraveling direction of the magnetic head. This means that the easy axisof magnetization is directed more toward a direction transverse to thetraveling direction of the read-write head than toward the travelingdirection. Also, preferably, the underlayer of the perpendicularrecording medium has a substantially radial or transverse anisotropy,which means that the magnetization in the soft magnetic material of theunderlayer are directed more toward a direction transverse to thetraveling direction of the read-write head when there is no externalmagnetic field applied to the SUL than toward the traveling direction.

Typically, when a magnetic recording medium is a tape, the tape travelsand the head is stationary. Therefore, a traveling direction of themagnetic head of a stationary head of a recording device in which themagnetic recording tape moves is the direction in which the head“travels” spatially with respect to the magnetic recording tape.

In accordance with embodiments of this invention, the substrates thatmay be used in the embodiments of the invention include glass,glass-ceramic, aluminum/NiP, metal alloys, plastic/polymer material,ceramic, glass-polymer, composite materials or other non-magneticmaterials. Glasses and glass-ceramics generally exhibit high resistanceto shock.

A preferred embodiment of this invention is a perpendicular recordingmedium comprising at least two amorphous soft magnetic underlayerswithout a spacer layer between the laminations of the underlayers. Theamorphous soft magnetic underlayer should preferably be made of softmagnetic materials and the recording layer should preferably be made ofhard magnetic materials. The amorphous soft magnetic underlayer isrelatively thick compared to other layers. A layer between the amorphoussoft magnetic underlayer and the recording layer is called an interlayeror an intermediate layer. An interlayer can be made of more than onelayer of non-magnetic materials. The purpose of the interlayer is toprevent an interaction between the amorphous soft magnetic underlayerand recording layer. An interlayer could also promote the desiredproperties of the recording layer. Longitudinal recording media do nothave an amorphous soft magnetic underlayer. Therefore, the layers namedas “underlayer” of longitudinal media are somewhat equivalent to theintermediate layer(s) of perpendicular media.

In the first and second magnetic underlayers structure according to theembodiments of the invention, both layers should preferably havesuitable soft magnetic properties, such as high saturation flux density,Bs (>600 emu/cc), and high magnetic permeability, μ (>100). The top SULshould provide suitable surface topographic property, chemistry, andcrystallographic property for the seed layers, interlayers and recordinglayers to grow on. FeCoB is a suitable top soft magnetic underlayermaterial.

One embodiment of this invention allows the use of a reduced number oflayers. Compare for example FeCoB/Ta/FeCoB, CZN/Ta/CZN, CZN/Ta/FeCoB toCZN/FeCoB in the table below. In particular, this embodiment could allowthe use of no spacer layer between the first SUL and the second SUL.

Another embodiment of this invention has a first SUL with lowmagnetostriction, no stripes, high Bst, high yield, and the second SULcould be relatively thin to avoid stripes and limit yield loss. Thesecond SUL could provide a template for oriented the magnetic recordinglayer such that the magnetic recording layer has less than 4°, morepreferred, less than 3.5°, most preferred, less than 3° of FWHM of XRDrocking curves around (0002) peaks. An example of this embodiment isCZN/FeCoB compared to FeCoB striped or CZN in tables below. The bottomSUL features less defect formation, resulting in fewer defects in thefilms due to target spitting etc. and/or does not need a spacer layerbetween layers that form the bottom SUL, if the bottom SUL is made up ofmultiple layers, and/or between the bottom and the top soft magneticunderlayers. Some of the SUL structure comprises spacer layers to have alaminated structure with spacer layers between the SUL laminations. Whenthe thickness of some SUL materials, for instance, SUL materials withlarge magnetostriction constant, is more than a critical thickness,stripe domains will form in the SUL. The SUL with spacer layers can havetotal thickness more than the critical thickness for the formation ofstripe domains of single SUL. The spacer layers prevent the build up ofhigh stress levels in the SUL. Spacer layers can be used for otherpurposes also. The spacer layer used here is non-magnetic, and does notprovide antiferromagnetic coupling between the underlayers adjacent tothe spacer layers. The thickness of spacer layers is 0.5 to 5 nm. InTables I and II, Ta layers are used as spacer layers. The soft magneticmaterials with low magnetostriction constant are the preferredcandidates for the bottom SUL and can be used for SUL withoutlamination. CoZr₅Nb₄ in the thickness range of 80 to 300 nm is anexample for the bottom SUL.

The underlayer and magnetic recording layer could be sequentiallysputter deposited on the substrate, typically by magnetron sputtering,in an inert gas atmosphere. A carbon overcoat could be typicallydeposited in argon with nitrogen, hydrogen or ethylene. Conventionallubricant topcoats are typically less than about 20 Å thick.

A adhesion layer, which could be optionally added as a layer lying inbetween the substrate and the soft magnetic underlayer, can enhance theadhesion of the SUL to the substrates and often control anisotropy ofthe soft magnetic underlayer by promoting a microstructure that exhibitseither short-range ordering under the influence of a magnetron field ordifferent magnetostriction. An adhesion layer could also alter localstresses in the soft magnetic underlayer.

Amorphous soft magnetic underlayers could produce smoother surfaces ascompared to polycrystalline underlayers and additionally may improve thecrystallographic orientations of the HCP-structured interlayers and hardmagnetic recording layers. Therefore, amorphous soft magnetic underlayercould be one way of improving the crystallographic and magneticproperties of the magnetic recording media for high-densityperpendicular magnetic recording. The amorphous soft magnetic underlayermaterials include CoZrNb, CoZrTa, a Cr-doped or non-dopedFe-alloy-containing underlayer, wherein the Fe-alloy could be FeTaC,CoFeZr, CoFeTa, FeCoZrB, FeCoC, FeCoTaZr and FeCoB.

Another advantage of amorphous materials as soft magnetic underlayermaterials is the lack of long-range order in the amorphous material.Without a long-range order, amorphous alloys have substantially lowermagnetocrystalline anisotropy. The use of amorphous soft magneticunderlayer could be one way of reducing noise caused by ripple domainsand surface roughness. The average surface roughness Ra of the amorphoussoft magnetic underlayer is preferably below 0.4 nm, more preferablybelow 0.3 nm, and most preferably below 0.2 nm as measured by highresolution Atomic Force Microscopy (AFM).

In accordance with the embodiments of the invention, if a particulartest method has not been explicitly stated to determine a parameter,then a conventional method used by persons of ordinary skill in this artcould be used to determine that parameter.

In the embodiments of this invention, the preferred range of theabsolute value of magnetostriction constant of the first SUL is <5*10⁻⁶.

In the embodiments of this invention, the preferred range of coercivityof the magnetic recording media is 3000 to 8000 Oe, more preferably,4500 to 6500 Oe.

The advantageous characteristics attainable by the embodiments of theinvention are illustrated in the following examples.

EXAMPLES

All samples described in this disclosure were fabricated with DCmagnetron sputtering except carbon films were made with ion beamdeposition.

Table I shows glide yield of media of 3 nm Cr/SUL/1.5 nm Cu/18 nmRuCr/12.8 nm CoPtTiO/4.5 nm carbon. All media were fabricated underotherwise identical conditions except the soft magnetic underlayerstructure. Each lamination of FeCoB and CoZrNb has thickness of 80 nmand 90 nm respectively except for the thickness specified on the table.Table I demonstrates that the perpendicular media with FeCoB SUL havemuch lower glide yield than that of the media with CoZrNb media.

TABLE I Glide yield of perpendicular media with different soft magneticunderlayers. FeCoB and CoZrNb and FeCoBOx total CoZrNbOx total Amount ofdiscs Amount of glide- SUL type thickness (nm) thickness (nm) for glidetest passed discs Yield (%) [CoZrNbOx]₃/CoZrNb 0 360 26 18 69[FeCoBOx/Ta]₂/FeCoB 240 0 34 9 26 [CoZrNbOx]₂/CoZrNb/Ta/FeCoB 54 270 2215 68

Table I shows that the media with the SUL comprised with thick CoZrNband thin FeCoB have glide yield similar to that of pure CoZrNb. Theletters Ox in the CoZrNbOx and FeCoBOx represent that the surfaces ofCoZrNb and FeCoB were exposed to oxygen immediately subsequent todeposition. In the laminated structure having Ta in Table I, Ta is aspacer layer. Note the high yield of the SUL with less thickness ofFeCoB, which is a material showing relatively higher incidence of defectformation.

Table II shows coercivity and FWHM (Full Width at Half Maximum) of XRD(X-ray Diffraction) rocking curves around (0002) peaks of RuCr/Co-alloyof the media with various SUL. All the media comprise 3 nm Cr/SUL/1.5 nmCu/18 nm RuCr/12.8 nm CoPtTiO/4.5 nm carbon deposited on Al/NiPsubstrates and fabricated under otherwise identical conditions exceptthe soft magnetic underlayer structure. The coercivity of these mediavaries slightly. The crystallographic orientations of these media varysignificantly. The media with CoZrNb SUL have much wider FWHM than themedia with FeCoB SUL. The media with thick CoZrNb and thin FeCoB at thetop of the SUL have similar or narrower FWHM, which is desirable, thanthat of media with FeCoB SUL. Note that Samples D to F have spacerlayers, but Sample F does not. In Sample E, the Ta layer is a spacerlayer.

TABLE II Coercivity and FWHM of XRD rocking curves around (0002) peaksof RuCr/Co-alloy of the media with various SUL. CoZrNb and FeCoB andCoZrNbOx total FeCoBOx total Sample thickness thickness Hc FWHM ID SULtype (nm) (nm) (kOe) (degrees) A CoZrNbOx/CoZrNb 180 0 5.908 4.84 B[CoZrNbOx]₂/CoZrNb 270 0 5.865 5.20 C [CoZrNbOx]₃/CoZrNb 360 0 5.7395.41 D [FeCoBOx/Ta]₂/FeCoB 0 240 5.812 3.14 E[CoZrNbOx]₂/CoZrNb/Ta/FeCoB 270 54 5.926 2.89 F [CoZrNbOx]₂/CoZrNb/FeCoB270 54 6.020 2.87

FIG. 4 shows erasure of media D, E, and F listed on table II testedunder various write current. Recording test shows that these three kindsof media have similar signal-to-noise ratio. The media with dual SULaccording to the embodiments of the invention can have better/lowererasure than that of the media with single alloy FeCoB SUL.

FIG. 5 shows optical HDI images of samples C (top), D (Middle) and F(bottom) listed on table II measured with p-polar channel and in phasemode display range 10. The images demonstrate that there are not obviousdomain walls in the SUL.

Magnetic hysteresis loops of media C, D, and F all show radial magneticanisotropy of the soft magnetic underlayers with easy axis along theradial directions of the discs. In the preferred embodiment, themagnetic recording layers have perpendicular anisotropy. The SUL hasin-plane anisotropy, and radial easy axis direction.

Media with CoZrNb/FeCoB first and second magnetic underlayers withoutsurface treatment of CoZrNb have similar magnetic performances andcrystallographic properties with those of media with FeCoB single alloySUL. For instance, the media similar with sample F, but withoutlamination of CoZrNb and without surface treatment, have FWHM of 3.13degrees. DC noise of such media is similar with the media with laminatedFeCoB SUL and with Ta spacer layers.

This application discloses several numerical range limitations thatsupport any range within the disclosed numerical ranges even though aprecise range limitation is not stated verbatim in the specificationbecause this invention can be practiced throughout the disclosednumerical ranges. Finally, the entire disclosure of the patents andpublications referred in this application are hereby incorporated hereinin entirety by reference.

1-20. (canceled)
 21. A magnetic stack comprising: a substrate; a firstsoft magnetic underlayer and a second soft magnetic underlayer on thesubstrate without a spacer layer between the first and second softmagnetic underlayers; and a magnetic recording layer, wherein the secondsoft magnetic underlayer is between the first soft magnetic underlayerand the magnetic recording layer, wherein the magnetic stack includesone or both of: a third soft magnetic underlayer between the substrateand the first soft magnetic underlayer; and at least one of the softmagnetic layers is configured to provide a template for orienting themagnetic recording layer.
 22. The magnetic stack of claim 21, comprisingthe third soft magnetic underlayer between the substrate and the firstsoft magnetic underlayer.
 23. The magnetic stack of claim 22, wherein atleast one of the soft magnetic layers is configured to provide thetemplate for orienting the magnetic recording layer.
 24. The magneticstack of claim 21, wherein at least one soft magnetic layer configuredto provide a template for orienting the magnetic recording layer. 25.The magnetic stack of claim 21, wherein the first and second softmagnetic underlayer are directly in contact with each other.
 26. Themagnetic stack of claim 21, wherein: the substrate is disc shaped; andthe soft magnetic underlayers have an easy axis of magnetizationdirected substantially in a radial direction of the disc shapedsubstrate.
 27. The magnetic stack of claim 21, wherein the magneticrecording layer has a growth direction with less than 4° full width halfmaximum (FWHM) of x-ray diffraction (XRD) rocking curves around the(0002) peaks.
 28. The magnetic stack of claim 21, wherein the first andsecond underlayers contain substantially no stripe domains.
 29. Themagnetic stack of claim 21, wherein the first soft magnetic underlayercomprises a material having low magnetostriction.
 30. The magnetic stackof claim 29, wherein the first soft magnetic underlayer material isselected from the group consisting of CoZrNb, CoZrTa, and combinationsthereof.
 31. The magnetic stack of claim 21, wherein the first softmagnetic underlayer comprises a material with an absolute value ofmagnetostriction constant of less than 5*10⁻⁶.
 32. The magnetic stack ofclaim 21, wherein at least one of the first and second soft magneticunderlayers comprises a substantially amorphous material.
 33. Themagnetic stack of claim 21, wherein at least one of the first and secondsoft magnetic underlayers is immediately oxidized subsequent todeposition.
 34. The magnetic stack of claim 21, wherein the second softmagnetic underlayer comprises FeCoB, FeCrCoB, FeTaC, CoFeZr, CoFeTa,FeCoZrB, FeCoC, FeCoTaZr, FeCrTaC, CoFeCrZr, CoFeCrTa, FeCoCrZrB,FeCoCrC, and FeCoCrTaZr.
 35. The magnetic stack of claim 21, wherein thefirst and second magnetic underlayers contain substantially no stripedomains and the combined Bst of the first soft magnetic underlayer andthe second soft magnetic underlayer is greater than 0.001 Gauss*Meter.36. A method comprising: depositing a soft underlayer structureincluding a first soft magnetic underlayer and a second soft magneticunderlayer without a spacer layer between the first and second softmagnetic underlayers; depositing a magnetic recording layer, the secondsoft magnetic underlayer arranged between the first soft magneticunderlayer and the magnetic recording layer, wherein depositing the softunderlayer structure includes one or both of: depositing a third softmagnetic underlayer between the substrate and the first soft magneticunderlayer; and depositing at least one soft magnetic layer configuredto provide a template for orienting the magnetic recording layer. 37.The method of claim 36, comprising depositing a third soft magneticunderlayer between the substrate and the first soft magnetic underlayer.38. The method of claim 37, comprising depositing at least one softmagnetic layer configured to provide a template for orienting themagnetic recording layer.
 39. The method of claim 36, comprisingdepositing at least one soft magnetic layer configured to provide atemplate for orienting the magnetic recording layer.
 40. The method ofclaim 36, wherein the first and second soft magnetic underlayers aredirectly in contact with each other.